Metal-Spine Conductivity in a Partially Oxidized Metallomacrocycle: (Phthalocyaninato)cobalt Iodide

Abstract

Oxidation by iodine of (phthalocyaninato)cobalt(II), Co(pc), affords the title compound, Co(pc)I, which is comprised of metal-over-metal columnar stacks of partially (1/3) oxidized Co(pc) groups that are surrounded by chains of I3- ions. Co(pc)I crystallizes in space group D24h—P4/mcc of the tetragonal system with a = 13.927 (1) A, c = 6.247 (1) A, V = 1212 A3, and Z = 2. The value of R on Fo2 for 66 variables and 540 observations is 0.055. Results of physial measurements, in particular the sign of the thermoelectric power, show the metal centers to be the site of oxidation. Charge transport thus proceeds along one-dimensional chains of metal atoms, as in the linear-chain platinum compounds. Strong interactions among the partially oxidized metal centers of the cobalt spine force the Co(pc) subunits to adopt an anomalously small interplanar spacing (3.12 A). They lead to an approximately temperature-independent susceptibility that is associated with strong Coulomb correlations in a one-dimensional cobalt dz2 band. The room-temperature conductivity of Co(pc)I is σ ~ 50 Ω-1 cm-1, which is comparable with that of the best Pt-spine conductors despite the fact that cobalt is a first transition series element at a much greater Co-Co spacing (3.12 A) than that (~2.95 A) for the conductors based on the third transition series element, Pt. Although the reflectivity shows a sharp edge at 6 X 103 cm-1, it provides evidence for a small band gap. The temperature response of the conductivity of Co(pc)I is nonmetallic (dσ/dT> 0), whereas that of the isostructural Ni(pc)I is metallic. These differences can be understood by considering the effects of potentials from the I3- chains on conduction bands with different occupancies, 1/3 filling for Co(pc)I but 5/6 filling for Ni(pc)I. © 1985, American Chemical Society. All rights reserved.